This post was written by one of our contributors; medical student w/ BSc in human nutrition + MSc in clinical and public health nutrition – Rebecca Fox
Caffeine is recognized as one of the world’s most consumed psychoactive substances (1). According to the National Diet and Nutrition Survey, UK adults, on average, consume around 130 mg/day of caffeine (around 1.5 cups of coffee or 3 cups of tea per day) (2,3).
With those statistics in mind, it’s safe to say that most of us consume caffeine regularly in one form or another. But is it actually good for us?
What is it?
Caffeine is a substance that stimulates the central nervous system, muscles, and heart. It works by blocking a molecule called adenosine from binding to its receptor. Adenosine normally has a number of different effects depending on its location in the body (4). For example, in the brain it helps promote sleep, and in the heart it aids in reducing heart rate. So, when caffeine comes along and blocks adenosine, you’re left with some major effects including increased feelings of wakefulness, and increased blood pressure.
Some people tend to react more to the effects of caffeine than others. Factors such as age, gender, weight, hormonal fluctuations, certain diseases, smoking, diet, genetics, medications, and regular caffeine consumption all play a role in determining how your body responds to caffeine (5).
Where is it found?
Caffeine is naturally found in a wide variety of foods including (6, 7):
- Coffee beans 🌱
- Black tea ☕️
- Green tea 🍵
- Yerba mate 🌿
- Chocolate 🍫
The concentration of caffeine in these foods naturally varies. For example, a 237 mL cup of brewed coffee, has around 100 mg of caffeine compared to the same size cup of black tea which has around 50 mg(3). Further, the processing of these beverages makes a difference in determining how much caffeine you take in. For example, coffee beans that have been roasted longer may have a deeper flavour, but a lower caffeine content compared to a lighter roast (8).
In addition to natural sources, there are a number of beverages, foods, and even medications that contain added caffeine (9). In fact, even decaffeinated beverages such as coffee and tea often have a little bit of caffeine left in them as a result of processing (20).
There are many supposed health benefits of caffeine ranging from improving athletic performance to preventing type 2 diabetes. While some of these effects have been proven, others still require further study:
- Migraines and Headaches: Caffeine’s effect on migraines appears mixed. On one hand, certain analgesics (pain relievers) that target migraines often contain a bit of caffeine combined with aspirin or acetaminophen as it is recognized to be helpful in treating certain types of migraines. On the other hand, the absence of caffeine may trigger migraines for individuals who consume caffeine regularly (i.e.getting a headache after missing your regular morning ‘cuppa)(10, 11).
- Alertness: If you’re a regular coffee or tea drinker you’re probably aware of how caffeine keeps your attention at a focus. One study went a little bit further and looked at the effects of combining caffeine with glucose (sugar). It appears that combining caffeine and a bit of food energy seems to improve mental alertness better than caffeine alone- just another reason to have breakfast with that cup of coffee (12).
- Athletic Performance: Caffeine consumption prior to exercise appears to improve endurance and feelings of physical strength while reducing feelings of exertion in both adults and adolescents (13). These effects may be affected by the dose and what time of day caffeine is consumed. For example, there may be a link between improved athletic performance for morning caffeine + exercise rather than evening exercisers (14). In addition, it has been shown that caffeine intake prior to high intensity interval training (HIIT) may increase metabolic rate as well as improve glycogen storage after exercise (22).
It’s also important to note that many studies looking at the effects of caffeine use coffee as their study tool. Coffee is one of the most widely consumed beverages and also has a naturally high concentration of caffeine- making it a convenient study tool. However, coffee also contains many other compounds such as antioxidants that have been associated with health benefits (15, 16). So, it’s important to remember that while caffeine itself may play a role in these effects, the drink itself may also have other benefits that are unaccounted for.
There’s always a flipside. While caffeine may have some health benefits (in addition to it being a mainstay in our morning beverages), there are some reasons to stay off the stuff:
- Pregnancy: The NHS recommends limiting caffeine to no more than 200 mg per day if you are pregnant. That’s approximately 2 cups of instant coffee. This limit is recommended as high levels of dietary caffeine have been associated with low birth weight babies as well as increased risk of miscarriage (2).
- Disturbed Sleep: Consuming lots of caffeine before bed may affect how well you’re able to doze off. It has been shown that caffeine consumed even 6 hours before bed has the ability to disrupt sleep(17). So, if you’re an evening coffee or tea drinker, perhaps try switching to an herbal variety like chamomile to maximize sleep quality(18).
- Anxiety: It has been shown that consuming higher amounts of caffeine (>400mg/day) may be associated with increased feelings of general anxiety, especially in those who are predisposed to having anxiety (19).
- IBS: The British Dietetic Association’s most recent review of IBS has suggested that there isn’t quite enough evidence to make a recommendation about whether caffeine intake contributes to symptoms (21). That being said, there are many different foods and beverages that trigger IBS in some people but not others- including caffeine. A number of smaller studies have shown that frequent caffeine consumption may worsen symptoms for those who are already experiencing IBS (21). So, speak to your doctor or dietitian if you feel like caffeine might be making your symptoms worse.
The NHS has a few recommendations for caffeine based on demographics (2, 19):
- <400 mg/day for adults
- <200mg/day for pregnant women
- <2.5mg/kg/d for children and adolescent
- Caffeine is present in a number of commonly consumed foods, beverages, and medications.
- Different people metabolize and respond to caffeine uniquely. This is due to a variety of genetic and environmental factors such as how frequently you consume caffeine.
- Caffeine is largely safe for most people, and may have beneficial effects on reducing migraines, as well as improving mental and athletic performance.
- High levels of caffeine have been associated with birth defects, therefore, reducing caffeine intake during pregnancy is recommended.
- Caffeine in large amounts may affect sleep and anxiety levels in certain individuals
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(2) NHS. Should I limit caffeine during pregnancy? 2018 [Available from: https://www.nhs.uk/common-health-questions/pregnancy/should-i-limit-caffeine-during-pregnancy/.
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(16) Poole R, Kennedy OJ, Roderick P, Fallowfield JA, Hayes PC, Parkes J. Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. BMJ. 2017;359.
(17) Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine. 2013;9(11):1195-200.
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(21) McKenzie YA, Bowyer RK, Leach H, Gulia P, Horobin J, O’Sullivan NA, Pettitt C, Reeves LB, Seamark L, Williams M, Thompson J. British Dietetic Association systematic review and evidence‐based practice guidelines for the dietary management of irritable bowel syndrome in adults (2016 update). Journal of Human Nutrition and Dietetics. 2016 Oct;29(5):549-75.
(22) Gui Y, Shi X, Huang C, Yi S, Lin D. PO-304 Caffeine Supplementation Altered Metabolic Profiles in High-intensity Interval Training. Exercise Biochemistry Review. 2018 Oct 4;1(5).